BOINC credit is based on what's called "cobblestones" and is a measure of the amount of computing effort expended by a given system. The approx 7:1 ratio of WCG to BOINC is due to the difference in credit systems between the original UD client and how BOINC awards credit. On top of this some projects artificially pump their awarded credit to attract crunchers from other projects.
GPU and CPU really shouldn't be compared. GPUs are massively parallel and can do far more calcs in a given time than a CPU, so asking why an hour on one isn't the same as an hour on the other isn't a fair question at all.